Horary astrology is an ancient branch of horoscopic astrology by which an astrologer attempts to answer a question by constructing a horoscope for the exact time at which the question was received and understood by the astrologer. There is disagreement amongst horary astrologers as to whether to use the location of the person who asks the question - the querent - or the location of the astrologer. Normally they are in the same place, but in modern times many astrologers work online and by telephone. These days the querent could be in Australia and send an email with the question to an astrologer in Europe. The horoscope would in this case be radically different. Many European practitioners take the location of the querent, but there are strong voices in traditional English schools who advocate using the location of the astrologer.
The answer to the horary question might be a simple yes or no, but is generally more complex with insights into, for example, the motives of the questioner, the motives of others involved in the matter, and the options available to him.
The English astrologer William Lilly (1602-81) was the last major horary astrologer, and probably the best-known horary practitioner in history. His book Christian Astrology is in print and widely used in the modern day practice of horary astrology. Today, horary astrology is still used much more in the United Kingdom, with medium popularity remaining in America, Germany, France, and the other Western European nations. Influential modern practitioners of horary astrology following Lilly's technique include UK astrologers Olivia Barclay, founder of the Qualifying Horary Practitioner (QHP), Barbara Dunn, Principal of QHP John Frawley, (runs courses), Deborah Houlding, Principal of STA, Susan Ward, Principal of a horary diploma course, and American astrologers J. Lee Lehman, (runs courses), and Christopher Warnock (runs courses).
Typically, a horary chart is read by first assigning the thing asked about, the quesited, to a particular house in the chart. For instance, asking "Where is my lost dog?" would be represented by the sixth house, as it is the house that governs small animals (traditionally, smaller than a goat). The house cusp of the sixth house will be in a particular sign, for example Libra. Libra is ruled by Venus, so Venus is considered the significator of the lost dog. Venus's state in the horoscope (its dignity, aspects, etc.) will give clues to the animal's location.
As a metaphor, consider an actor who breaks his leg on opening night; essential good, accidentally debilitated. The converse is true. A planet in poor essential dignity may have considerable accidental power. Taking the earlier example of Mars, if Mars was in Scorpio, and in an angular house in the horary chart (1st, 7th, 10th, 4th) then it is considered accidentally as well as essentially strong. It has quality, and power to act, to express.
Reception refers to how each planet in a horary question chart "view" or "receive'" each other, either favourably, unfavourably, or somewhere in between. If Mars is in Taurus, and Venus is in Scorpio, then each of the planets is in the sign the other planet rules. (Venus is ruler of Taurus, Mars of Scorpio). This is called mutual reception by rulership, and although each planet is in its detriment, it nevertheless receives the other planet favourably. In some horary questions, a thorough understanding of receptions (and the above example skims the surface of this topic) is required to delineate the interplay of how the various significators view each other what sort of attitudes are taking place in the area of the question.